1. Chapter 9 Objectives Section 1 Mendel’s Legacy
Describe how Mendel was able to control how his pea plants were pollinated.
Describe the steps in Mendel’s experiments on true-breeding garden peas.
Distinguish between dominant and recessive traits.
State two laws of heredity that were developed from Mendel’s work.
Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes.

2. Section 1 Mendel’s Legacy
Chapter 9
Gregor Mendel
The study of how characteristics are transmitted from parents to offspring is called genetics.
Mendel is considered to be the “father” of genetics because of all of his work with heredity
Heredity is the passing of traits from parents to their offspring

3. Gregor Mendel, continued
Section 1 Mendel’s Legacy
Chapter 9
Gregor Mendel, continued
Mendel’s Garden Peas
Mendel observed characteristics of pea plants.
Traits are genetically determined variants of a characteristic.
Each characteristic occurred in two contrasting traits.

4. Gregor Mendel, continued
Section 1 Mendel’s Legacy
Chapter 9
Gregor Mendel, continued
Mendel’s Methods
Self-pollination occurs when pollen is transferred from the anthers (male) of a plant to the stigma (female) of the same plant
Cross-pollination occurs when pollen is transferred between flowers of two different plants
Mendel controlled his experiments by manually pollinating the other plants through cross-pollination, he removed anthers from the plants he was working with

5. P F1 F2 Chapter 9 Mendel’s Experiments
Section 1
Chapter 9 P
Mendel’s Experiments F1 F2
Mendel bred plants for several generations that were true-breeding (self-pollinating) for specific traits and called these the P generation. (parental)
True breeding pea plants always produce offspring each of which can have only one form of a trait
Ex. True-breed pea plants with yellow pods will self-pollinate and produce offspring with yellow pods
Offspring of the P generation were called the F1 generation.
Offspring of the F1 generation were called the F2 generation.

6. Three Steps of Mendel’s Experiments
Section 1 Mendel’s Legacy
Chapter 9
Three Steps of Mendel’s Experiments
Pg 175 Figure 9-3

7. Mendel’s Results and Conclusions
Section 1 Mendel’s Legacy
Chapter 9
Mendel’s Results and Conclusions
Recessive and Dominant Traits
Mendel concluded that inherited characteristics are controlled by factors that occur in pairs.
In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.

8. Mendel’s Results and Conclusions, continued
Section 1 Mendel’s Legacy
Chapter 9
Mendel’s Results and Conclusions, continued
The Law of Segregation
The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes.
Law of segregation is used to describe how traits can disappear and reappear in a certain pattern from generation to generation

9. Mendel’s Results and Conclusions, continued
Section 1 Mendel’s Legacy
Chapter 9
Mendel’s Results and Conclusions, continued
The Law of Independent Assortment
The law of independent assortment states that factors for individual characteristics are distributed to gametes independently of one another.
The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.

10. Support for Mendel’s Conclusions
Section 1 Mendel’s Legacy
Chapter 9
Support for Mendel’s Conclusions
We now know that the factors that Mendel studied are alleles, or alternative forms of a gene.
One allele for each trait is passed from each parent to the offspring.
We can see this by looking at ourselves in comparison to our parents, we may have some of both our mother and father
We will study this further with Punnett Squares in 9-2

11. Homework
Section 9.1 Review Pg 178 #1-8

12. Chapter 9 Objectives Section 2 Genetic Crosses
Differentiate between the genotype and the phenotype of an organism.
Explain how probability is used to predict the results of genetic crosses.
Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses.
Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait.
Differentiate a monohybrid cross from a dihybrid cross.

13. Genotype and Phenotype
Section 2 Genetic Crosses
Chapter 9
Genotype and Phenotype
The genotype is the genetic makeup of an organism.
EX: RR, rr, Rr,
The phenotype is the appearance of an organism.
EX: The chicken is red (the allele for red feather color is dominant)
Homozygous – when both alleles of a pair are alike
“ R R ” or “ r r “
Heterozygous – when two alleles in a pair are different
“ R r ”

14. Probability = number of times an event is expected to happen
Section 2 Genetic Crosses
Chapter 9
Probability
Probability is the likelihood that a specific event will occur.
A probability may be expressed as a decimal, a percentage, or a fraction.
Probability of drawing a red marble
Probability = 2 red marbles = 2 = 1
8 marbles total
Probability = number of times an event is expected to happen
number of times an event could happen

15. Predicting Results of Monohybrid Crosses
Section 2 Genetic Crosses
Chapter 9
Predicting Results of Monohybrid Crosses
A Punnett square can be used to predict the outcome of genetic crosses.
A cross in which one characteristic is tracked is a monohybrid cross.
Genotypic ratio is the ratio of genotypes that appear in offspring
Phenotypic ratio is the ratio of offspring’s phenotypes

16. Monohybrid Cross of Heterozygous Plants
Section 2 Genetic Crosses
Chapter 9
Monohybrid Cross of Heterozygous Plants

17. Chapter 9 Y = Yellow y = Green (non-yellow)
Section 2 Genetic Crosses
Chapter 9
Y = Yellow
y = Green (non-yellow)
What is the genotypic ratio for this monohybrid cross?
What is the phenotypic ratio for this monohybrid cross?

18. Chapter 9 Y = Yellow y = Green (non-yellow)
Section 2 Genetic Crosses
Chapter 9
Y = Yellow
y = Green (non-yellow)
What is the genotypic ratio for this monohybrid cross?
1:2:1
What is the phenotypic ratio for this monohybrid cross?
3 yellow : 1 green 3:1

19. Chapter 9 Predicting Results of Monohybrid Crosses, continued
Section 2 Genetic Crosses
Chapter 9
Predicting Results of Monohybrid Crosses, continued
A testcross, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.
R ? x rr

20. Chapter 9 Predicting Results of Monohybrid Crosses, continued
Section 2 Genetic Crosses
Chapter 9
Predicting Results of Monohybrid Crosses, continued
Complete dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype.
Ex. Both pea plants PP and Pp for flower color have purple flowers
PP or Pp

21. Section 2 Genetic Crosses
Chapter 9
Predicting Results of Monohybrid Crosses, continued
Incomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait.
In four o’clock flowers, red flowers (R) self-pollinate and only produce red offspring, while white flowers (R’) self-pollinate and only produce white offspring
IF, red (R) and white (R’) are crossed they will produce 100% pink (RR’) offspring RR
R’R’
RR’

22. Chapter 9 Predicting Results of Monohybrid Crosses, continued
Section 2 Genetic Crosses
Chapter 9
Predicting Results of Monohybrid Crosses, continued
Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring.
Four human ABO blood types, A, B, and AB and O, are determined by three alleles. The letters A and B refer to two molecules on the surface of the red blood cell. The genotype of a person with blood type AB is IAIB, and neither allele is dominant over the other type. Type AB blood cells carry both A- and B-types of molecules on their surface.

23. Predicting Results of Dihybrid Crosses
Section 2 Genetic Crosses
Chapter 9
Predicting Results of Dihybrid Crosses
A cross in which two characteristics are tracked is a dihybrid cross.
To create this type of cross we will use the FOIL method to be used in a 4x4 Punnett Square

24. Section 2 Genetic Crosses
Chapter 9
Dihybrid Crosses

25. Homework
Section 9.2 Review Pg 186 #1-7